1 Field of the Invention
This invention relates to shock absorbers of the hydraulic type. More particularly, it relates to rotary shock absorbers wherein an internal vane attached one part of the shock absorber rotates at a variable rate in a fluid-filled cylindrical chamber to force the fluid under pressure through one or more orifices located in a baffle thereby providing shock-dampening properties. This invention finds special adaptation and use in the field of motorcycles.
2 Description of the Prior Art
Shock absorbers are devices that dampen or attenuate the shock introduced to a vehicle when the wheels strike projections or potholes in the roadway. Shock absorbers are normally used in conjunction with springs to assist in dampening the shock for the purpose of providing a more comfortable ride in the vehicle.
Shock absorbers are constructed in two main types. The elongated "cylinder-piston and rod" type is the more common and comprises an axially aligned cylinder filled with a fluid, a piston slidably received therein and a rod attached to the piston wherein the piston moves through the fluid, transferring fluid from above to below the piston, or vice versa, through various orifices in the piston, either of a set size or under spring tension to provide for a greater opening depending upon the intensity of the shock applied to the rod. These devices are used where there is sufficient space provided between the vehicle frame member and the oscillatory member to position the shock for reciprocating extension therebetween.
The other general type, namely the rotary-vane shock absorber, comprises a fluid-filled cylinder containing a fixed baffle and a moveable vane thus dividing the cylindrical chamber into two subchambers. One or more apertures are provided in either the baffle or the vane or both so that a torque applied to a rotatable center shaft through a lever arm connected to an oscillatory member of the frame will cause them to move closer together or further away from each other forcing fluid through the orifices from one subchamber to another thereby attenuating the shock occasioned to the lever arm.
For the most part, rotary vane shock absorbers are linear in response as the vane is attached directly to the center shaft without restraint thereby providing for direct application of torque, coming from the oscillatory member through a lever arm connected to the shaft, to the vane and through to the fluid to force the fluid through the orifice. While these shock absorbers find use in various areas, especially in crowded areas where imposition of the long cylindrical shock absorber would be difficult, there has not been much development beyond the mere linearity of their construction.
Nonlinearity or nonlinear response in hydraulic shock absorbers is often desired to provide a soft ride at low vehicle speeds, where movement of the pivot arm is substantial, and thereafter to provide a stiffer ride at high speeds when movement is to be minimized so that the vehicle holds better to the roadway. This property, while existing in cylinder-piston and rod type shock absorbers, is substantially absent in the vane type. There is a definite need, therefore, for a rotary vane-type hydraulic shock absorber displaying non-linear shock absorbing qualities.
Especially in certain vehicles, such as motorcycles, that are subjected to high speeds and high shock loads, there is the need for a stout, rotary-vane type hydraulic shock absorber for use in the crowded area of the motorcycle frame that will involve less travel than in normal cylinder-piston and rod shock absorbers where the deflection of the piston rod is often created due to the excessive loads applied to the oscillatory member. Further, because virtually all of the rotary-vane type shock absorber components are housed in a sealed, cylindrical chamber filled with lubricating oil, the parts are not subject to corrosive environments as are the piston-type shock absorbers. Finally, in such vehicles as motorcycles, which are ridden over a variety of surfaces under different conditions, ranging from soft rides on smooth surfaces to hard rides on very rough surfaces, there is a need for a shock absorber that displays the property of having the ride characteristics adjustable from outside the shock absorber so that by merely twisting or turning a dial, bolt or other element to make some manual adjustment, a complete change in the ride may be obtained. These sorts of functions are not found in the elongated cylinder-piston and rod type shock absorber.